The separation of ε- and γ’-phases in the plasma nitrided layer by colour etching techniques

Abstract

In this research, various etching reagents were tested on a quenched and tempered 42CrMo4 steel and an untreated C45E unalloyed steel sample, whichwere plasmanitrided for 4 h at 490 °C with 75% N2–25% H2 gas mixture. The aim is to find a reagent suitable for revealing and separating the two ε- and γ’-phases in the nitrided layer. Previously, the compound layer’s composition could only be identified by X-ray diffraction (XRD), a costly, time-consuming and not easily accessible process. Therefore, finding an alternative could be crucial for small businesses. Nital, Picral, Villela, and Oberhoffer’s reagents were investigated in the experiments. Scanning electron microscope (SEM) was used to observe the nitrided layer, and it was analysed by XRD to detect the formed phases and electron dispersive X-ray spectroscopy (EDS) was used to analyse the elemental composition. Nital is the most common used etchant in the industry, but Oberhofferwas found to be an excellent etchant to separate the two phases in a dual phases nitrided layer.